1. Field of Invention
The invention relates to a current control device and, in particular, to a current control device for controlling a current of a motor.
2. Related Art
Motors are widely used in fans or various types of electrical devices. However, if an operating current of the motor is too high for a long time, the motor tends to burn out.
Referring to FIG. 1, a fan motor controller 11 generates driving currents 112 to 115 according to a rotating speed controlling signal 111. A fan motor 12 includes a coil 121 and a plurality of transistors 122, 123, 124 and 125. Driving currents 112, 113 114 and 115 are respectively inputted to the transistors 122 to 125 to control an operating current of the coil 121. An input voltage Vcc is electrically connected to sources of the transistors 122 and 123. One terminal of the coil 121 is electrically connected to the transistors 122 and 124. The other terminal of the coil 121 is electrically connected to the transistors 123 and 125. Emitters of the transistors 124 and 125 are electrically connected to a current sampler 13. The current sampler 13 samples current values from the emitters of the transistors 124 and 125. A comparator 141 compares a voltage of the sampled result of the current sampler 13 with a reference voltage Vref. When the sampled voltage is too high in comparison of the Vref, the two transistors 142 and 143 turn on to adjust the driving currents 114 and 115 and decrease the operating current of the coil 121.
Controlling the transistors 142 and 143 can decrease the operating current of the coil 121. It is possible to prevent the coil 121 from burning out due to the too-high operating current. However, the driving currents 114 and 115 generated by the fan motor controller 11 are not decreased. When the transistors 142 and 143 are disabled, the operating current of the coil 121 is still too high. Thus, the main reason of causing the too-high operating current of the coil 121 is not eliminated.
Therefore, it is an important subject of the invention to provide a current control device that can control the driving current for driving the motor, so as to prevent the too-high operating current of the motor caused by the improper control of the driving current, and thus to lengthen the lifetime of the motor.